1. Field of the Invention
The invention relates to a laminated pole for an electric machine having salient poles, the pole being clamped by clamping means, which clamping means comprise through bolts in the section of the pole close to the axis and flange-like pressure distribution elements at the end.
A laminated pole having these features is known, for example, from Swiss Patent Specification 632,877 and U.S. Patent Specification 4,316,111.
2. Discussion of Background
Rotor poles of electric machines with salient poles have been constructed to be solid or laminated (stacked pole) depending on the electric or mechanical loading. Solid poles of forged steel or steel casting exhibit higher stray losses due to the relatively low ohmic resistance. Stray losses in this case essentially means the eddy current losses caused by the higher field harmonics caused by the armature current, and the pulsation losses caused by the main field due to the slotting. Solid poles act like conductor rods of a cage armature winding so that large currents can flow in them with asynchronous operating conditions.
Due to the capability of carrying large currents and the high energy dissipation capacity, the solid pole is particularly suitable for asynchronous starting of large synchronous motor generators.
Laminated poles have a high ohmic resistance in the longitudinal direction, the stray losses are correspondingly lower but so is their damping effect. The stacked pole is therefore provided with a damper winding to obtain the required operational stability. Stamped single laminations of a thickness of about 1 mm are used for producing stacked poles. The laminations are stacked over a mandril in a press. After the high axial compression pressure has been reached, the mandril is welded to solid pole end plates at both end faces. The high pressure per unit area and additional welds at the outer contours result in a mechanically compact body which does not have to be subjected to any further machining since the construction of the support claws, venting slots, support noses for the pole winding and so forth is contained in the stamping and stacking operations (inhouse publication "Synchronous machines for hydroelectric power plants" CH-T 130 082 D from 1977 of BBC Aktiengesellschaft Brown Boveri and Cie, Baden/Schweiz, particularly page 32).
The pole end plates made of solid steel require a comparatively elaborate production method for slow-running synchronous machines and for switchable-pole machines, particularly for hydroelectric generators having high numbers of poles. In addition, they impair the effects on the operating characteristics of the machine resulting from the lamination of the pole body and indicated above.
The laminated pole according to Swiss Patent Specification 632,877 avoids the above inadequacies by laminating and welding-together of the pole end plates. This reduces the production expenditure by about 40 to 50 % of that when solid pole end plates are used. A further advantage consists in that the pole end plate has a lighter weight since the fill factor is .ltoreq.98 % due to the lamination. This weight saving is accompanied by a reduction in the loading on the pole anchorages. In addition, the pulsation losses of the end plate laminated in accordance with the invention are lower than those of a solid construction.
The pole plates exhibit a thickness of between 40 and 60 mm, depending on the axial length of the pole body, and are built up out of single laminations with a thickness of up to 3 mm and are welded to one another at several points at least at the outer contour. The lamination thickness corresponds to that of the pole laminations of the pole body. They have the same outer contours as the pole laminations of the pole body and can thus be processed with one and the same stamping tool.
Apart from through holes for clamping the entire pole, the laminations of the pole end plates exhibit one or more recesses which are flush with one another and through which bolts of appropriate cross-section are pushed which, in turn, are welded to the single laminations at the two end faces of the pole end plate. They are used as end supports for the pole coils.
On the basis of the prior art, the present invention is based on the object of creating a laminated pole of the type initially mentioned, which exhibits all advantages of the known pole and furthermore can also be produced more economically and simply.